1. Field
Example embodiments relate to semiconductor substrates and methods of manufacturing the same. Also, example embodiments relate to low-defect semiconductor substrates having low defect densities and an excellent surface morphology property and methods of manufacturing the same.
2. Description of Related Art
GaN is a wide bandgap semiconductor having a direct transition type bandgap of 3.39 eV and has been studied to be used in a variety of optoelectronic devices including blue light-emitting devices and protective thin films from the early 1970s. Since GaN has a continuous high solubility with a III-V-based nitride semiconductor such as InN or AlN, a trivalent nitride solid solution such as InxGa(1-x)N or GaxAl(1-x)N can be formed. And, since a bandgap is changed into a primary function for composition according to the composition of a ternary nitride, by adjusting the composition of the III-V-based nitride semiconductor, a light-emitting device or a light-receiving device including all visible regions from a red wavelength region to a ultraviolet wavelength region can be manufactured.
Since such a GaN thin film may be used in a variety of fields, the importance of study and developing of growth of a GaN thin film and a device using the same has been recognized a long time ago and has proceeded. During this time, heteroepitaxy has been studied. In heteroepitaxy, a different kind of substrate, such as sapphire (α-Al2O3), having large lattice mismatching and large thermal expansion coefficient mismatching with respect to GaN so as to grow a good GaN thin film and a GaN epitaxial layer, is grown using a buffer layer, such as AlN or GaN, so as to alleviate mismatching of lattice parameter and thermal expansion coefficient.
However, when GaN is grown on the different kind of substrate, a GaN or AlN buffer layer should be used at a low temperature of 500° C.-600° C. so as to alleviate lattice parameter and thermal expansion coefficient mismatching with respect to the substrate. As a result, an epitaxial growth process is complicated and the growth of various compounds such as InN or GaN required for manufacture of a light-emitting device may be not easily performed. In particular, due to differences between lattice parameter and thermal expansion coefficient, a GaN thin film grown on a sapphire substrate includes many lattice defects, that is, a dislocation density of about 109 defects/cm2. As a result, the performance of the manufactured light-emitting device may be degraded. However, the defect density of a GaN-based optoelectronic device, such as a light-emitting diode (LED) or laser diode (LD), should be low so as to increase a life time thereof and so as to improve reliability thereof. In the case of a traditional substrate having a low defect density, GaN is grown thick using halide or hydride vapor phase epitaxy (HVPE) growth and then is separated to be used as a GaN substrate. In this method, the GaN substrate does not have a sufficiently low defect density, nor is it easy to grow GaN sufficiently large to a size at which GaN can be used as a substrate. Thus, as a method of manufacturing a low-defect GaN thin film, a method for reducing a defect density by performing lateral growth has been spotlighted. Examples include epitaxial lateral overgrowth (ELOG) and Pendeo-epitaxy.
However, like ELOG, when a mask such as SiO2 or SiNx is used, due to a difference in surface tension between a grown GaN thin film and the mask, crystals are tilted so that defects may be generated in a coalesced boundary of the GaN thin film. In this procedure, a groove may be formed on the surface of the GaN thin film and, thus, a surface morphology property may be deteriorated. Due to the insertion of a different kind of material such as SiO2 or SiNx, strain may be nonuniformly distributed in the GaN thin film. In addition, since thermal conductivity of SiO2 is lower than that of GaN, thermal reliability of a device implemented on a mask region may be degraded. Accordingly, in order to address these problems, the development of a new technology for manufacturing a low-defect semiconductor substrate having a low defect density and an excellent surface morphology property is needed.